Modern Deformation and Uplift in the Sisters Region

In 2001, scientists discovered that a broad (10 by 20 km, or 6 by 12 mi) area focused 5–6 km (3–
4 mi)
west of the summit of South Sister had been rising at an average rate of 3–5 cm (1–2 in) per year
since late
1997. Close monitoring of the area by satellite and ground-based methods showed that the rate of
uplift
decreased to about 1.4 cm (0.5 in.) per year during 2004–2006 and to less than 1.0 cm (0.4 in.) per
year
by 2013. Modeling of the uplift (inflation) suggests that it was caused either by the intrusion of
about 20
million cubic meters (26 million cubic yards) of magma at about 5-km (3-mi) depth or by rise of a
hot,
buoyant plume of water and gas to a similar level that caused heating and expansion of surrounding
rock.
In either case, an eruption is unlikely in the near future if current trends continue. Similar inflation
episodes have been recognized at many volcanoes around the world, and others probably went
unnoticed
before the development of modern monitoring techniques such as GPS and InSAR.